Background and Objective: Fractional photothermolysis (FP) is a new concept using arrays of microscopic thermal damage patterns to stimulate a therapeutic response. We analyzed epidermal and dermal response to FP with the aim of correlating histological and clinical response. Study Design/Materials and Methods: Twelve subjects received a single treatment with a prototype diode laser emitting at a wavelength of 1,500 nm, delivering 5 mJ per microscopic treatment zone (MTZ), and a density of 1,600 MTZs/cm 2 on the forearm. Biopsies were procured over a period of 3 months. The biopsies were analyzed by two blinded dermatopathologists using hematoxylin and eosin (Hematoxylin and Eosin Stain), Elastica von Gieson, nitro-blue-tetrazolium-chloride (NBTC) viability, and immunohistochemistry stains. Furthermore, the treatment sites were evaluated in vivo by confocal microscopy. Results and Discussion: Twenty-four hours after fractional photothermolysis, the continuity of the epidermal basal cell layer is restored. Complete epidermal regeneration is obtained 7 days after the treatment. Microscopic epidermal necrotic debris (MENDs) are seen as early as 1 day after FP. MENDs contain melanin pigment, and are shed from the epidermis within 7 days. Evidence of increased collagen III production is shown with immunohistochemistry (IHC) staining 7 days after FP. IHC for heat shock protein 70 (HSP 70) shows the expression of HSP 1 day after FP, and IHC for alpha smooth muscle actin shows the presence of myofibroblasts 7 days after FP. These findings are concordant with the induction of a wound healing response by FP. There is no evidence of residual dermal fibrosis 3 months after treatment. Conclusion: A single treatment with fractional photothermolysis induces a wound healing response in the dermis. A mechanism for the precise removal of epidermal melanin is described, in which MENDs act as a melanin shuttle.

Direct heat exposure to cells causes protein degradation and DNA damage, which can lead to genetic alteration and cell death, but little is known about heat-induced effects on the surrounding tissue. After burns or laser surgery, loss of viability in the surrounding tissue has been explained by a temperature gradient due to heat diffusion. This study shows that, in the absence of any direct heating, heat diffusion, or cell-to-cell contact, "bystander" cells that share the medium with heat-exposed cells exhibit DNA damage, apoptosis, and loss of viability. We coin this phenomenon "active thermal bystander effect" (ATBE). Significant ATBE was induced by fibroblasts exposed for 10 minutes to a temperature range of 44-50 degrees C (all P<0.011). The ATBE was not induced by cells heated to lethality above 54 degrees C and immediate medium exchange did not suppress the effect. Therefore, the thermal bystander effect appears to be an active process in which viable, heat-injured cells induce a signal cascade and/or mediator that damages or kills surrounding bystander cells. The ATBE may have clinical relevance for acute burn trauma, hyperthermic treatments, and distant tissue damage after localized heat stress.

Background Lasers and intense pulsed light sources (IPLS) are proposed for the treatment of many pigmentary disorders. They are sometimes considered as magic tools able to remove any type of lesions. Although being the best option for several hyperpigmented lesions, they can also worsen some conditions and have potential side‐effects. Objective The aim of this review was to give evidence‐based recommendations for the use of lasers and IPLS in the treatment of hyperpigmented lesions. Methods These recommendations were produced for the European Society of Laser Dermatology by a consensus panel made up of experts in the field of pigment laser surgery. Recommendations on the use of lasers and light treatments were made based on the quality of evidence for efficacy, safety, tolerability, cosmetic outcome, patient satisfaction/preference and, where appropriate, on the experts' opinion. Results Lasers and IPLS are very effective for treating many hyperpigmented lesions such as lentigos, dermal hypermelanocytosis or heavy metal depositions. In the other hand, they have to be considered with great caution for other disorders, such as café au lait macules, melasma or postinflammatory hyperpigmentation. After making the correct diagnosis, if lasers or IPLS are indicated, the optimal wavelengths and parameters will be chosen taking into account the skin phototype, origin and depth of the target pigments. Conclusion Although potentially very effective, lasers and IPLS cannot be proposed for all types of hyperpigmented lesions. In all cases, precise recognition of the disorder is mandatory for choosing between these devices and other therapeutic approaches.